Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing the same, and can be suitably utilized, for example, for a semiconductor device including a flash memory.
Description of the Background Art
Semiconductor devices such as a logic device are equipped with a nonvolatile flash memory that stores information. One form of the flash memory includes a select gate electrode, a floating gate electrode, a control gate electrode, an erase gate electrode, a source region and a drain region. This type of flash memory is disclosed in Patent Document 1 (Japanese Patent Laying-Open No. 2009-44164).
In the flash memory, information is written by applying a prescribed voltage to each of the source region, the control gate electrode, the select gate electrode and the drain region, to inject electrons into the floating gate electrode from the drain region. Information is erased by applying another prescribed voltage to the erase gate electrode, to draw the electrons stored in the floating gate electrode into the erase gate electrode.
Information is read by applying still another prescribed voltage to each of the control gate electrode, the select gate electrode and the drain region, to determine whether or not a current (read current) flows between the drain region and the source region. If the electrons have been stored in the floating gate electrode, very little read current flows. If the electrons have not been stored in the floating gate electrode, on the other hand, the read current flows. When the read current is low, an incorrect determination may be made as to whether or not information has been written. Thus, erase characteristics are considered to be important characteristics of a flash memory.